Mandrel for expanding internallyfinned tubes



April 19, 1949- A. w. HALLBERG MANDREL FOR EXPANDING INTERNALLY-FINNED TUBES Filed Oct. 30, 1947 Patented Apr. 19, 1949 MANDREL FOR EXPANDING INTERNALLY- FINNED TUBES August W. Hallberg, Waterbury, Conn., assignmto Chase Brass a Copper 00. Incorporated, Waterbury, Conn., a corporation Application October 30, 1947, Serial No. 783,076

3 Claims. 1

The present invention relates in general to the manufacture of finned heat-exchange tubes and more especially to a superior method and means for improving the physical characteristics of an internally-finned tube produced by hot extrusion techniques.

In general, internally-finned tubes produced by hot extrusion are quite soft and have very little rigidity, as a consequence of which the tubes, including their internal fins, are easily bent and rendered unsatisfactory for practical purposes. It is desirable, therefore, to impart an appreciable degree of rigidity to the internally-finned tubes and to straighten the fins so as to provide a product acceptable to the trade. Moreover, as extruded, the transverse dimensions of the finned tube may vary slightly throughout the length of the tube and from tube to tube and, hence, it is desirable to subject the tube to a sizing operationto produce accurately-dimensioned tubes.

An object of the present invention is to provide a superior method of imparting rigidity to hotextruded intemally-finned tubes.

A further object of the invention is to impart rigidity to a hot-extruded internally-finned tube by a cold-working operation wherein the tube is expanded radially in successive stages.

A still further object of the invention is to cold work an internally-finned tube by passing a mandrel therethrough having a stepped enlargement and longitudinal fin-receiving grooves whereby the tube is expanded radially and the I internal fins simultaneously straightened in one pass of the tool.

A still further object of the invention is to provide an improved mandrel for expanding an internally-finned tube while straightening the internal fins thereof.

A still further object of the invention is to provide an improved mandrel for cold working an intemally-finned tube wherein a stepped enlargement at one end of the mandrel expands the tube in progressive stages.

With the above and other objects in view, as will appear to those skilled in the art from the present disclosure, this invention includes all features in the said disclosure which are novel over the prior art.

In the accompanying drawings, in which cersimultaneously 2 tain modes of carrying out the present invention are shown for illustrative purposes:

Fig. 1 is a perspective view of a finned tube formed by a hot-extrusion process and characterizedby both internal and external fins;

Fi 2 is a side elevation in section of the tube on line 2-2 of Fig. 1 and including a portion of the improved mandrel for cold working the tube;

Fig. 3 is an end elevation of the tube and mandrel on section line 3-3 of Fig. 2; and

' Fig. 4 is a perspective view of the improved mandrel for cold working the finned tube.

Referring to the drawings, the type of internally-finned tube to which the improved method of this invention is applied is indicated in Fig.

1 and comprises a cylindrical body-portion III of any desired length having internal fins II which project inwardly radially from the inner wall of the body ID of the tube and extend longitudinally thereof, In the present embodiment,

each fin is substantially rectangular in cross secv tion and there are eight fins in number, but it will be appreciated that these specific features do not limit the application of the invention. Moreover, the tube shown in Fig. 1 has a plurality of longitudinal external fins I! which extend outwardly radially from the outer surface of the tube, the number of external fins being twice the number of internal fins II and every other external fin being in substantial alignment radially with one of the internal fins. The number 01' external fins may vary, of course, from the number shown and, in fact, the invention is equally applicable to an internally-finned tube having no external fins.

The finned tube is generally formed of a ductile metal such as copper or a copper-base alloy and by a hot-extrusion process such as described more fully in my copending application, Serial No. 713,160 filed November 29, 1946, and issued as Patent No. 2,461,640 on Feb. 15, 1949.

In practicing the improved method of this invention, a length of the hot-extruded internallyfinned tube is held securely on a draw-bench, whereupon a mandrel or other suitable tool is drawn through the tube from one end thereof to the other to expand the tube radially, the radial expansion of the tube being effected in successlve stages, each of progressively greater diameter and in one pass of the tool, whereby the tube is cold worked to such a degree as to have the rigidity required by the trade. The degree of cold working is measured, in general, by the amount or radial expansion of the tube and the characteristic feature of this invention is the discovery that the radial expansion of the tube must be eflected in two or more successive stages in order to control the size of the tube. Hence, the ultimate radial expansion necessary for building the required rigidity into the tube is accomplished in successive stages, the initial stage effecting a relatively slight increase in the diameter of the tube and the next succeeding stages effecting progressively greater increases in the diameter of the tube, the ultimate increase in diameter of the tube for cold working the tube sufliciently to produce the rigidity required being substantially of its original diameter.

Simultaneously with the cold working of the tube, the body "I of the tube and its internal fins II are straightened. To the latter end, the mandrel or expanding tool is provided with longitudinal recesses or grooves spaced circumferentially around the tool at distances corresponding to the circumferential spacing of the internal fins of the tube. Thus, as the tool is forced into one end of the finned tube, the internal fins are adapted to engage in the longitudinal recesses or grooves of the tool, whereby movement of the tool and, in particular, its grooves relative to the tube, effectively straightens its fins.

As shown especially well in Figs. 2 and 4, the tool is comprises a substanti'ally-cylindrical bodyportion ll having a drawbar l5 fixedly secured to one end thereof in alignment with its longitudinal axis for pulling the tool through the finned tube by means well known in the art.

The body ll of the tool is substantially cylindrical and for superior performance is a few thous'andths larger than the internal diameter of the tube l0. Although the body ll of the tool will thus expand the tube radially slightly, the cold working accomplished thereby is insuflicient to impart any appreciable rigidity to the tube, the slightly greater diameter of the body-portion ll of the tool constituting, primarily, means for straightening the finned tube as the tool is pulled therethrough from one end to the other.

In this connection, it has been discovered that the over-all length of the body of the tool must be a multiple of its diameter for eifectively straightening the tube.

Formed integrally or in any other suitable manner at one end of the body-portion ll of the tool is an enlarged cylindrical head, hereinafter referred to as a stepped annular enlargement, which is adapted to cold work the inner wall of the tube to build the required rigidity into the tube in one pass of the tool therethrough. This stepped annular enlargement of the tool is indicated generally at l6 and comprises two successive concentric annular flanges or steps I! and II of progressively increased transverse dimensions, that is to say, the diameter of the inner flange or step I! is several thousandths greater than the diameter of the body-portion ll of the tool, while the diameter of the outer flange or step I8 is equally again as great as the diameter of the inner step. The outer step it is blended to the adjacent section of the inner step II by a radius 19, the inner step I! being blended, in turn, to an adjacent section of the body-portion ll of the tool by a radius 20.

The specific dimensions of the tool and, in particular, the transverse dimensions of its stepped enlargement are in large measure determined by the size of the tube being cold worked and the degree of cold working necessary to accomplish the required rigidity. For the purpose of illustration, however, the diameter of the body of a tool for cold working an internally-finned tube of substantially three-quarter inch outside diameter and one-sixteenth inch wall thickness is from about 0.005 inch to about 0.010 inch greater than the internal diameter of the tube, the diameter of the inner annular flange of the stepped enlargement bein about 0.031 inch greater than the diameter of the body l0 and the diameter of the outer annular flange being about 0.031 inch greater than the diameter of the inner annular flange. The longitudinal dimension of the stepped enlargement I6 is preferably a fraction of the over-all length of the tool and in the embodiment shown is substantially 10% thereof.

As pointed out above, the tool also embodies means for receiving the internal fins of the tube and for straightening the fins during the coldworkin operation on the tube. To this end, a plurality of longitudinal recesses or grooves 2! are formed in the tool, each recess extending throughout the combined lengths of the bodyportion I4 and enlarged head l6 of the tool and each groove bein spaced apart circumferentially from its neighboring grooves a distance corresponding to the circumferential spacing of the internal fins H of the tube, whereby the fins are adapted to engage therein. The body of the tool is thus divided into a plurality of longitudinal sectors equally spaced circumferentially about the longitudinal axis of the tool. Moreover, each groove 2| corresponds in cross section substantially to the cross-sectional dimensions of the internal fins ll of the tube, although the depth of each groove is slightly greater than the transverse dimensions of its respective internal fin H, as shown clearly in Fig. 3. Consequently, as the grooves are moved longitudinally relative to the tube, the internal fins of the tube will be straightened.

By practicing the above described method by means of the particular tool shown and described herein, internally-finned tubes are adapted to be transformed from their relatively soft and unstraightened condition as extruded to a perfectly straight tube which has been cold worked by radial expansion to acquire a relatively-high degree of rigidity. Moreover, during the coldworking operation performed by the tool IS, the tube III has been sized to a predetermined diameter to within very close tolerances while the internal fins ll of the tube have been straightened.

The invention may be carried out in other specific ways than those herein set forth without departing from the spirit and essential characteristics of the invention, and the present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.

I claim:

1. A mandrel for cold working an internallyfinned tube comprising: a tube-enlarging bodyportion; a stepped annular enlargement at one end of said body of progressively increased diametcrs; and a plurality of fin-receiving grooves extending longitudinally of said body-portion and said stepped enlargement.

2. A mandrel for cold working an internallyfinned tube comprising: a tube-enlarging bodyportion, the over-all length of said body-portion being a multiple of its diameter; a stepped annular enlargement at one end of said body of progressively increased diameter and constituting a fraction of the length of said body-portion: and a plurality of fin-receiving grooves extending longitudinally of said body-portion and said stepped enlargement.

3. A mandrel for coincidentally straightening and hardening the body and fins of an internallyfinned tube, said mandrel comprising a cylindrical body-portion and an annular enlargement at one end thereof of greater diameter than the diameter of said body-portion; and a plurality of longitudinal tin-straightening grooves extending throughout the length of said body-portion and said enlargement so that when said mandrel is pulled through an internally-finned tube of less diameter than the diameter of said annular enlargement, said tube is straightened and hardened.

AUGUST W. HAILBERG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 485,691 Harrington Nov. 8, 1892 734,264 Hock July 21, 1903 1,304,954 Foster May 27, 1919 1,646,384 Bergstrom Oct. 25, 1927 1,813,096 Stenner July 7, 1931 2,173,665 Sibley Sept. 19, 1939 2,281,207 Schoen Apr. 28, 1942 2,298,379 Hofiman Oct. 13, 1942 2,357,123 Maxwell Aug. 29, 1944 2,367,226 Lonsdale Jan. 16. 1945 FOREIGN PATENTS Number Country Date Germany Aug. 13, 19.37 

